My mistake. I did not read the Text.CSV.ByteString document carefully. parseCSV requires a strict ByteString, but I was feeding a lazy one. Have a good weekend! Hong On Fri, Nov 6, 2009 at 3:47 PM, Hong Yang wrote:

I have the following code:

$$$$$$$$ module Main where

import System.Environment (getArgs) import Text.CSV.ByteString import qualified Data.ByteString.Lazy.Char8 as L

main = do [args] <- getArgs file <- L.readFile args let result = parseCSV file case result of Nothing -> putStrLn "Error when parsing!" Just contents -> do putStrLn "parsing OK!" -- map_header_records contents $$$$$$$$

which yielded the error as follows:

Couldn't match expected type `Data.ByteString.Internal.ByteString' against inferred type `L.ByteString' In the first argument of `parseCSV', namely `file' In the expression: parseCSV file In the definition of `result': result = parseCSV file

readFile in the Data.ByteString.Lazy.Char8 module returns ByteString type. Since the module is qualified as L, L.readFile returns L.ByteString. But parseCSV expects a ByteString. Sometimes this is annoying, because it makes type matching difficult (at least for me, a beginner). I really wish Haskell can intelligently treat L.ByteString, M.ByteString, and whatever X.ByteString the same as ByteString, and match them.

Can someone tell me how to solve the above problem?

Thanks,

Hong